A semiconductor wafer, e.g., a silicon wafer, for use in fabrication of a semiconductor device and the like is chamfered by grinding an edge portion in order to avoid chipping due to handling, and also subjected to mirror edge polishing based on polishing as a particle generation countermeasure in a device process in recent years. However, when a mechanical damage in the chamfer portion is deep, a damage or a grinding striation remains even though mirror edge polishing is performed, which results in a factor of particle generation.
Thus, as a method for reducing a mechanical damage in the chamfer portion, there is a method for performing so-called helical grinding with respect to a chamfer portion of a wafer, for example, while inclining a resin bond grinding stone (a resin grinding stone) with respect to the wafer (see Japanese Patent Application publication No. H05-152259).
In regular grinding, a chamfer portion is ground in a state where a main surface of a wafer W becomes vertical to a rotating axis of a resin grinding stone 13 as shown in FIG. 3(A), but in this case, grinding striations 14 in a circumferential direction are apt to be generated in the chamfer portion as shown in FIG. 3(B).
On the other hand, when performing helical grinding, the chamfer portion of the wafer W is ground in a state where the rotating axis of the resin grinding stone 13 is inclined with respect to a rotating axis of the wafer W as shown in FIG. 4(A). When such helical grinding is performed, while weak grinding striations 15 are generated in an oblique direction in the chamfer portion of the wafer W as shown in FIG. 4(B), the chamfer portion of the wafer W contacts with the surface of the grinding stone 13, thus an effect of improving surface roughness of the chamfer portion as compared with regular grinding is obtained.
However, if the chamber portion of the wafer is subjected to helical grinding by using the resin grinding stone as explained above, a reduction in damages in the chamfer portion of the wafer and an increase in a grinding stone life can be achieved, whereas there is a problem that vertical symmetry of the chamfer portion of the wafer considerably collapses. When the chamfer portion is continuously machined in particular, upper and lower angles of a groove of the resin grinding stone gradually vary, and asymmetry of the chamfer portion of the wafer is thereby more increased.